Characterization of Osmotic Membranes

Dear Colleagues,

The performance of osmosis membranes such as water flux, salt rejection, and resistance to fouling and chlorine attack is governed by membrane structure, morphology, chemical composition, and physicochemical properties. As such, membrane characterization is very important in the design of new membrane materials and optimizing membrane fabrication protocols. Membrane characterization is also very important to understand the mechanisms of transport in osmotic membranes.

The structure of the selective layer, which determines the transport properties of osmotic membranes, cannot be observed directly. Nevertheless, techniques such as positron annihilation spectroscopy (PALS), small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron spin resonance (ESR) provide useful information about internal and surface structures of the osmotic membranes. Surface chemistry is typically characterized by Fourier transform infrared (FTIR) spectroscopy, electron dispersive X-ray spectroscopy (EDX/EDS), and X-ray photoelectron spectroscopy (XPS). In addition, a contact angle analyzer measures surface hydrophilicity/hydrophobicity, which affects permeate flux, salt rejection, and membrane fouling. Another important factor, which has a profound effect on fouling propensity and separation performance, is the surface charge, which is characterized by zeta potential. In the specific case of forward osmosis (FO) membranes, characterization of the support layer is as important as the characterization of the selective layer

There are two groups of mechanistic models describing transport in osmotic membranes. The models from the first group assume that osmotic membranes have a microporous top layer; they include the following: preferential sorption-capillary flow (PS-CF), finely porous (FP), surface force-pore flow (SF-PF), and modified surface force-pore flow (MD-SF-PF) models. The models from the second group assume that RO membranes have a nonporous top layer; they include the solution-diffusion (SD), the extended solution-diffusion (ESD), and the solution-diffusion-imperfection (SDI) models. Of these, the simplest and most commonly used is the SD model. However, the results of sophisticated membrane characterization techniques are more commonly related to the ultimate reverse osmosis (RO) and FO performance of the membranes (permeate flux, solute rejection, reverse solute flux) rather than to basic transport properties in the SD model, such a solubility, diffusivity, and permeability coefficients of solute and solvent.

This Special Issue focuses on recent advances in the characterization of osmotic membranes and, in particular, on linking the transport properties of membranes with the results of sophisticated characterization techniques at the fundamental level. Authors are invited to submit their latest results. Original papers, communications, and reviews are welcome.

Prof. Boguslaw Kruczek
Guest Editor

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• Thin-film composite (TFC) and nanocomposite (TFN) membranes
• Integrally skinned asymmetric membranes
• Reverse osmosis
• Forward osmosis
• Pore characterization
• Physicochemical characterization
• Performance characterization
• Solution-diffusion models
• Pore-flow models
• Concentration polarization
• Solubility, diffusivity, and permeability
• Influence of support layer